1. Field of the Invention
This invention relates to engine exhaust purification systems, and more particularly to apparatuses, systems and methods for regenerating diesel engine particulate filters.
2. Description of the Related Art
Engine exhaust emission standards required by regulatory agencies typically monitor the release of diesel particulate matter, nitric oxides, and unburned hydrocarbons. A critical emission of gasoline or other stoichiometric engines is carbon monoxide. Catalytic converters have been implemented in exhaust gas after-treatment systems for spark-ignition engines, though historically such aftertreatment systems have often not been added to diesel engines. To remove particulate matter emanating from the latter, particularly in light of recently announced emissions standards, typically a diesel particulate filter is installed downstream from or in conjunction with a catalytic converter.
A common particulate filter comprises a porous ceramic matrix with parallel passageways through which exhaust gas passes. Particulate matter, usually ash and soot, accumulates on the surface of the filter, creating a buildup that must eventually be removed to prevent obstruction of the exhaust gas flow. Ash, a residue of burnt engine oil, is substantially incombustible and builds slowly within the filter. Soot, chiefly composed of carbon, refractory and not easily wiped away, can be oxidized and driven off of the filter in a regeneration process. In most applications soot accumulates much faster than ash, to the extent that an estimate of the rate of soot accumulation is substantially equivalent to an estimate of the rate of total particulate accumulation.
Various conditions, including but not limited to engine operating conditions, mileage, driving style, terrain, etc., affect the rate at which the engine produces particulate matter and the rate at which such matter accumulates within a diesel particulate filter. Notwithstanding this variability, existing systems typically regenerate the filter at set intervals of time or distance.
A controlled regeneration can be initiated by the engine's control system when a predetermined amount of particulate has accumulated on the filter, when a predetermined time of engine operation has passed, or when the vehicle has driven a predetermined number of miles. Oxidation from oxygen (O2) generally occurs on the filter at temperatures above about 400 degrees centigrade, while oxidation from nitric oxides (NO2), sometimes referred to herein as noxidation, generally occurs at temperatures between about 250 C and 400 C. Controlled regeneration typically consists of driving the filter temperature up to O2 oxidation temperature levels for a predetermined time period such that oxidation of soot accumulated on the filter takes place.
A controlled regeneration can become uncontrolled if the oxidation process drives the temperature of the filter upwards more than is anticipated or desired, sometimes to the point beyond which the filter substrate material can absorb the heat, resulting in melting or other damage to the filter. Less damaging uncontrolled or spontaneous regeneration of the filter can also take place at noxidation temperatures, i.e., when the filter temperature falls between about 250 C and 400 C. Such uncontrolled regeneration generally does not result in runaway temperatures, but can result in only partial regeneration of the soot on the filter. Partial regeneration can also occur when a controlled regeneration cannot continue because of a drop in temperature, exhaust gas flow rate, or the like. Partial regeneration and other factors can result in non-uniformity of soot distribution across the filter, resulting in soot load estimation inaccuracies and other problems.
As noted above, typical controlled regenerations are lock-step affairs, occurring with limited input as to driving, engine, or filter conditions that might impact the regeneration profile, including when the regeneration should occur, when it should end, and how it should take place. Such practices can result in fuel inefficiencies and shortened filter life.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method for adapting a filter regeneration profile based on relevant conditions.